1. Field of the Invention
The present invention relates to a resin molding apparatus and a resin molding method, and more specifically to a resin molding apparatus and a resin molding method in which a thermoplastic resin material is press-molded.
2. Description of the Related Art
It is known that thermoplastic resin materials are molded by, for example, injection molding. Injection molding is one of a plurality of suitable methods for large scale production due to its extremely short molding cycles compared to other molding methods. According to injection molding, thermoplastic resins are heat-melted in injection molding machines, kneaded mechanically with, e.g., screws, and injected to metal molds. The metal molds are then cooled and molded articles are obtained. Another compression molding method, called stamp forming, may also be used. According to stamp forming, fiber-reinforced thermoplastic composite materials are heated to a melting point or higher of thermoplastic resins at the outside of metal molds to melt thereof, charged to metal molds at a temperature lower than the melting point of thermoplastic resins and subjected to compression molding in presses. The heating apparatuses used for stamp forming may be, for example, far-infrared heaters (IR heaters).
Japanese Patent Publication No. 3947560 suggests a method of press molding in which a composite sheet of a thermoplastic resin non-woven fabric combined with continuous reinforcement fibers is provided in a metal mold. As a heating apparatus of the metal mold, an electromagnetic induction-type heating apparatus is described.
Thermoplastic resin materials (e.g., fiber-reinforced thermoplastic composite materials) are considered to be useful in the future as materials for applications such as computer housings or automotive outer panels because they are lighter than metals such as iron or aluminum and they have certain strength. However, stabilization of the quality thereof and improvement in productivity are required in order to be in practical use for these applications.
When molding thermoplastic resin materials, it may be desirable to maintain the length of reinforcement fibers contained in the resins in order to improve mechanical properties (e.g., flexural strength, tensile strength) of molded articles. In order to stabilize the quality of molded articles, it is desirable to control the orientation of reinforcement fibers as much as possible. According to conventional injection molding, melted resin materials are kneaded mechanically with, e.g., screws and injected into metal molds in injection molding machines. In this case, reinforcement fibers contained in the resin materials are cut by screws upon mechanical kneading of melted resin materials, making it difficult to keep the length of reinforcement fibers in the resin materials long. It is also very difficult to control the orientation of the reinforcement fibers because they are injected into metal molds in injection molding machines.
Stamp forming, one of the other molding methods, requires steps of pre-heating and molding thermoplastic resin materials, so that there are limitations to shorten the molding cycle. It also has drawbacks in working efficiency such as handling of thermoplastic resin materials after a heating step.
According to Japanese Patent Publication No. 3947560, an electromagnetic induction-type heating apparatus is used as a heating apparatus of the metal molds. However, such an apparatus heats the molds by electromagnetic induction, so that the apparatus configuration is enlarged as well and is more complex. There is also a loss of energy upon generation of inductive current, increasing total energy required for molding. Thus, this method is susceptible to improvement in terms of energy saving and the like.